The present disclosure relates to electronic devices, and more particularly, to data storage systems.
Semiconductor memory devices are microelectronic devices that are used to design digital logic circuits such as microprocessor-based applications and computers for the fields ranging from satellite to consumer electronics. Therefore, an advance in memory fabrication technology, including technology development and process improvement obtained through scaling for high speed and high integration density, assists in establishing the performance standards of other digital logic systems.
Semiconductor memory devices are generally classified into volatile memory devices and nonvolatile memory devices. Examples of the volatile memory devices include static random-access memory (SRAM) devices and dynamic random-access memory (DRAM) devices. The SRAM devices store logic information by setting the logic state of a bistable flip-flop, and the DRAM devices store logic information by charging a capacitor. The volatile memory devices store and read data in a power-on state, but lose the stored data in a power-off state.
Examples of the nonvolatile memory devices include magnetic read-only memory (MROM) devices, programmable read-only memory (PROM) devices, erasable programmable read-only memory (EPROM) devices, electrically erasable programmable read-only memory (EEPROM) devices, and flash memory devices. The nonvolatile memory devices can retain data stored therein even when power supply thereto is interrupted. The state of data stored in the nonvolatile memory devices may be permanent or reprogrammable according to memory fabrication technologies. The nonvolatile memory devices are used to store programs and microcodes in various applications such as computers, avionics, communications, and consumer electronic technologies. A combination of volatile and nonvolatile memory storage modes in a single chip may also be used in devices such as nonvolatile RAMs (nvRAMs) in a system that requires quick and reprogrammable nonvolatile memories. In addition, specific memory structures including some additional logic circuits have been developed to optimize the performance for application-oriented tasks.
Since nonvolatile memory devices such as MROM devices, PROM devices and EPROM devices are not allowed to erase and write, it is not easy for general users to update data stored in such nonvolatile memory devices. On the other hand, since nonvolatile memory devices such as EEPROM devices and flash memory devices are electrically erasable and programmable, their applications are expanding to auxiliary memory devices or system programming that require continuous data update.